Such packaging is discarded when the goods are put to use, and so it is desirable not only for the package itself to be inexpensive in so far as its materials and construction are concerned, but also for it to be applicable to and removable from the goods expeditiously and with a minimum of labour. Those desiderata are to some extent incompatible with the imperative that the package reliably exclude contaminants for what may be a lengthy period.
One widely adopted proposal to resolve that incompatibility has been to wrap or swathe the article or bundle in substantially impervious, pliable sheet or strip wrapping medium. An excellent wrapping medium for the purpose is so-called stretch wrap plastics film, which is chemically inert, proof to most liquids including water, and tends to cling to anything it contacts including itself. That film is stretched prior to or during its application to the article or bundle. It has the property known as "memory" which means it seeks to return to the unstretched state. As a result it tends to mould itself to the article and form a tight wrapping thereon.
One class of known apparatus for applying a pliable wrapping medium has comprised a turntable or the like on which the article is placed and a draw-off spool holder rotatably supporting a spool of the wrapping medium. In use, an end of the wrapping medium is taped or otherwise secured to the article and the article is rotated to draw wrapping medium from the spool holder and wrap itself therein. The spool holder includes tension regulating devices to maintain a suitable tension in the drawn-off medium and, in the case of stretch wrap film, to stretch it as it leaves the spool. The spool-holder (or the turntable) may be moved in the axial direction of the spool to cause successive turns of the wrapping medium applied to the article to overlap and so provide an uninterrupted coverage. As a general rule the article has to be reoriented on the turntable at least once during the wrapping to obtain full coverage. Alternatively, if the shape of the article permits, it may be continuously reoriented on the turntable as wrapping proceeds.
Disadvantages of this class of known wrapping apparatus are the limitations on the shapes of the articles that may be wrapped and the limitation on the mass of the article if the expense of providing a heavy duty turntable with high power drive and braking systems is to be avoided.
Another class of known apparatus which alleviates the last mentioned disadvantage provides a rotatable frame which supports the spool holder so that it may orbit about the article being wrapped. In this instance the article may be stationary except for such intermittent or continuous reorientation as may be needed for full coverage. For example, a cylindrical article may be supported on two spaced apart parallel rollers with their axes horizontal. At least one of those support rollers may be driven to cause the article to turn slowly about its own, also horizontal, axis. The spool holder may be set to orbit the article in a generally horizontal plane, but which may be raised or lowered, with the spool axis vertical. Depending on the altitude of the spool relative to the axis of the article, the drawn-off medium will cover the whole of the article or will leave uncovered a central circular area of greater or lesser diameter of each end face of the article. In the event that the cylindrical article is also annular, for example a coil of metal strip, those uncovered areas may be adjusted to substantially coincide with the ends of the bore of the coil.
The main disability of this last mentioned class of known apparatus is once again the limitation on the shape of the articles that may be conveniently wholly wrapped.
Another class of known wrapping apparatus particularly suited to wrapping elongate articles comprises a circular structure which carries a spool holder. That structure is caused to rotate about its own axis, which is horizontal, to produce orbital movement of the spool holder about that axis. The article to be wrapped is passed by appropriate conveyors through the structure along that axis.